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• Weaknesses of Hibernate

  - by Sinuhe

  I would like to know which are the weak points of Hibernate 3. This is not pretended to be a thread against Hibernate. I think it will be a very useful knowledge for decide if Hibernate is the best option for a project or for estimating its time. A weakness can be: A bug Where JDBC or PLSQL are better Performance issues ... Also, can be useful to know some solutions for that problems, better ORM or techniques, or it will be corrected in Hibernate 4. For example, AFAIK, Hibernate will have a very bad performance updating 10000 rows comparing to JDBC in this query: update A set state=3 where state=2

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• SQL Query to delete oldest rows over a certain row count?

  - by Casey

  I have a table that contains log entries for a program I'm writing. I'm looking for ideas on an SQL query (I'm using SQL Server Express 2005) that will keep the newest X number of records, and delete the rest. I have a datetime column that is a timestamp for the log entry. I figure something like the following would work, but I'm not sure of the performance with the IN clause for larger numbers of records. Performance isn't critical, but I might as well do the best I can the first time. DELETE FROM MyTable WHERE PrimaryKey NOT IN (SELECT TOP 10,000 PrimaryKey FROM MyTable ORDER BY TimeStamp DESC)

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• [Rails] Cross Browser Popup size woes

  - by stephemurdoch

  I need to display certain content inside a popup window, and the body element must be 320px by 300px for styling purposes So I do the following: %p = link_to "Play in popup", popup_podcast_path(@podcast), :popup => ['new_window','height=300,width=320,toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=no,resizable=yes'] Firefox does exactly what I ask it to do, it displays a popup window, with a page body that is 320px wide and 300px high, so my content fits perfectly inside. But Chrome includes the browser frame dimensions when sizing the popup, which means that the body element is less than the required size.... i.e. if the browser titlebar is 10px high, then this is subtracted from the space allocated to the body element How do I tell Chrome, that I want the body element to be 320 by 300, and that I dont want it to subtract the width and height of the browser frame from body element dimensions It's a bit like the old box-model problem where FF and IE added padding in different ways except firefox adds the browser frame outside the desired 320x300 size, and Chrome is adding it inside

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• flex - printing graphics

  - by rudi888

  Hello :) It's possible to print in flex image (high resolution png/jpg file) with print quality greater than 72DPI ??? rudi888

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• Best way to encrypt certain fiels in SQL Server 2008?

  - by Josh

  I'm writing a .net web app that will read and write information to a SQL 2008 backend database. Some of this information will be highly confidential in nature so I want to encrypt certain data elements. I dont want to use TDE or any full-database encryption for performance reasons. My main concern is protecting this sensitive data as a last resort against a SQL injection or even a database server compromise. My question is what is the best way to do this to preserve performance? Is it faster to use the SQL2008 encryption functions such as EncryptByKey, or would it be faster to encrypt and decrypt the data in the .NET web app itself using a symmetric key stored in the secure web.config and store the encrypted values in the DB?

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• fastest in-memory cache for XslCompiledTransform

  - by rudnev

  I have a set of xslt stylesheet files. I need to produce the fastest performance of XslConpiledTransform, so i want to make in-memory representation of these stylesheets. I can load them to in-memory collection as IXpathNavigable on application start, and then load each IXPAthNavigable into singleton XslCompiledTransform on each request. But this works only for styleshhets without xsl:import or xsl:include. (Xsl:import is only for files). also i can load into cache many instances of XSLCompiledTransform for each template. Is it reasonable? Are there other ways? What is the best? what are another tips for improving performance MS Xslt processor?

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• What are some best practises and "rules of thumb" for creating database indexes?

  - by Ash

  I have an app, which cycles through a huge number of records in a database table and performs a number of SQL and .Net operations on records within that database (currently I am using Castle.ActiveRecord on PostgreSQL). I added some basic btree indexes on a couple of the feilds, and as you would expect, the peformance of the SQL operations increased substantially. Wanting to make the most of dbms performance I want to make some better educated choices about what I should index on all my projects. I understand that there is a detrement to performance when doing inserts (as the database needs to update the index, as well as the data), but what suggestions and best practices should I consider with creating database indexes? How do I best select the feilds/combination of fields for a set of database indexes (rules of thumb)? Also, how do I best select which index to use as a clustered index? And when it comes to the access method, under what conditions should I use a btree over a hash or a gist or a gin (what are they anyway?).

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• ASMX Still slow after 'Generate serialization assembly'

  - by Buzzer

  This question is related to: http://stackoverflow.com/questions/784918/asmx-web-service-slow-first-request. I inherited a proxy to a legacy ASMX Service. Basically as the post above states, the first call performance is literally 10 times slower than the subsequent calls. I went ahead and turned on ‘Generate serialization assembly' on the project that contains the proxy. The 'serializers' assembly is actually generated. However, I haven't seen any performance increase at all. Do I need to do anything else other than make sure the 'serializers' assembly is in the client's bin directory? Do I have to 'link' the proxy to the 'serializers' assembly during proxy generation (wsdl.exe)? I guess I'm stuck at this point. J Saunders where u at? :)

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• Avoid implicit conversion from date to timestamp for selects with Oracle using Hibernate

  - by sapporo

  I'm using Hibernate 3.2.7.GA criteria queries to select rows from an Oracle Enterprise Edition 10.2.0.4.0 database, filtering by a timestamp field. The field in question is of type java.util.Date in Java, and DATE in Oracle. It turns out that the field gets mapped to java.sql.Timestamp, and Oracle converts all rows to TIMESTAMP before comparing to the passed in value, bypassing the index and thereby ruining performance. One solution would be to use Hibernate's sqlRestriction() along with Oracle's TO_DATE function. That would fix performance, but requires rewriting the application code (lots of queries). So is there a more elegant solution? Since Hibernate already does type mapping, could it be configured to do the right thing? Update: The problem occurs in a variety of configurations, but here's one specific example: Oracle Enterprise Edition 10.2.0.4.0 Oracle JDBC Driver 11.1.0.7.0 Hibernate 3.2.7.GA Hibernate's Oracle10gDialect Java 1.6.0_16

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• Quick convert XML to Excel

  - by Bajji

  What is the quickest (as in least effort, not super performance) way to convert 112K rows in XML to a Excel view.

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• How do I layout an image that will be dynamically sized in interface builder?

  - by Tony

  I am having trouble laying out scrollable view in interface builder. A screen shot of my layout is here. As you can see the layout is pretty simple. The UIImageView above the text will not have a specific height. It may be 100px high or 300px high. This is why the view is scrollable. I am experiencing two problems with this layout: 1) For some reason the image will sit behind the text instead of pushing it down. Take a look here. 2) The obvious other problem is that the upper most UIImage and UILabel are getting pushed up off of the screen. I am thinking this has to do with the UIScrollView but I haven't been able to figure out why. Thanks!

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• What's wrong with my logic here?

  - by stu

  In java they say don't concatenate Strings, instead you should make a stringbuffer and keep adding to that and then when you're all done, use toString() to get a String object out of it. Here's what I don't get. They say do this for performance reasons, because concatenating strings makes lots of temporary objects. But if the goal was performance, then you'd use a language like C/C++ or assembly. The argument for using java is that it is a lot cheaper to buy a faster processor than it is to pay a senior programmer to write fast efficient code. So on the one hand, you're supposed let the hardware take care of the inefficiencies, but on the other hand, you're supposed to use stringbuffers to make java more efficient. While I see that you can do both, use java and stringbuffers, my question is where is the flaw in the logic that you either use a faster chip or you spent extra time writing more efficient software.

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• how to apply Discrete wavelet transform on image

  - by abuasis

  I am implementing an android application that will verify signature images , decided to go with the Discrete wavelet transform method (symmlet-8) the method requires to apply the discrete wavelet transform and separate the image using low-pass and high-pass filter and retrieve the wavelet transform coefficients. the equations show notations that I cant understand thus can't do the math easily , also didn't know how to apply low-pass and high-pass filters to my x and y points. is there any tutorial that shows you how to apply the discrete wavelet transform to my image easily that breaks it out in numbers? thanks alot in advance.

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• How should I measure Concurrent Licence Usage

  - by Andrew Wood

  Hi I have detailed stats on user access to my system detailing login and logout times as well as machine used, network username etc. I am in need of measuring what I would term a concurrent user licences level based on this information. Now I could take the maximum logged in for any 1 day in a 3 month period say 170 or I could take the average say 133. Does anyone have or know of a formula for working this out or is it as simple as the high water mark which is 170 in my example. A client has recently gone from an unlimited licence to a concurrent licence so I am faced with the task of setting the initial licence level. There is potential for more licence sales in the future so I don't want it set to high and I do want it based on historical data that the system collects rather than guess work.

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• Getting differences between WVGA800 and WVGA854 in Android Emulator

  - by Droidy

  So far I just have one XML layout file, and one drawable directory, drawable-hdpi. I first want to target the high density screens. I added a bunch of imagebuttons to a relativelayout and everything looks perfect in the WVGA800 emulator. The problem arises when I view it in the WVGA854 emulator. Not only do the imagebuttons not position the same, but the images are blurry. I used dip for the layout margins on the imagebuttons even though it shouldn't matter in this case because WVGA800 and 854 are both high density. What is the problem? Why would it look totally different on emulators that have the same density and almost have the same exact screen dimensions? Thanks!

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• How to set that compiler flag?

  - by mystify

  Shark told me this: This instruction is the start of a loop that is not aligned to a 16-byte address boundary. For optimal performance, you should align the start of a hot loop using a compiler directive. With gcc 3.3 or later, use the -falign-loops=16 compiler flag. for (int i=0; i < 4; i++) { // line with the info //...code } How would I set that flag, and does it really improve performance?

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• iOS6 MKMapView using a ton of memory, to the point of crashing the app, anyone else notice this?

  - by Jeremy Fox

  Has anyone else, who's using maps in their iOS 6 apps, noticing extremely high memory use to the point of receiving memory warnings over and over to the point of crashing the app? I've ran the app through instruments and I'm not seeing any leaks and until the map view is created the app consistently runs at around ~3mb Live Bytes. Once the map is created and the tiles are downloaded the Live Bytes jumps up to ~13mb Live Bytes. Then as I move the map around and zoom in and out the Live Bytes continuos to climb until the app crashes at around ~40mb Live Bytes. This is on an iPhone 4 by the way. On an iPod touch it crashes even earlier. I am reusing annotation views properly and nothing is leaking. Is anyone else seeing this same high memory usage with the new iOS 6 maps? Also, does anyone have a solution?

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• Managing EntityConnection lifetime

  - by kervin

  There have been many question on managing EntityContext lifetime, e.g. http://stackoverflow.com/questions/813457/instantiating-a-context-in-linq-to-entities I've come to the conclusion that the entity context should be considered a unit-of-work and therefore not reused. Great. But while doing some research for speeding up my database access, I ran into this blog post... Improving Entity Framework Performance The post argues that EFs poor performance compared to other frameworks is often due to the EntityConnection object being created each time a new EntityContext object is needed. To test this I manually created a static EntityConnection in Global.asax.cs Application_Start(). I then converted all my context using statements to using( MyObjContext currContext = new MyObjeContext(globalStaticEFConnection) { .... } This seems to have sped things up a bit without any errors so far as far as I can tell. But is this safe? Does using a applicationwide static EntityConnection introduce race conditions? Best regards, Kervin

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• How would I go about building a calendar UI control for the iPhone/iPad?

  - by BeachRunnerJoe

  Hello. There are a few different 3rd party code frameworks that include calendar controls, but most of them have a lot of functionality I don't need, plus most of them lack sufficient documentation on how to use them and I'm not a proficient enough iPhone developer figure it out using just the code. So I'm going to attempt to build my own and I was hoping you could provide me with some high-level direction to get started. At a high level, how could I build a simple, calendar control that doesn't do much more than display a calendar (month view, with the current date highlighted) and allows the user to selected a date? Something that looks like the calendar in the upper right corner of this image... Thanks so much in advance for your help!

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• Virtual Function Implementation

  - by Gokul

  Hi, I have kept hearing this statement. Switch..Case is Evil for code maintenance, but it provides better performance(since compiler can inline stuffs etc..). Virtual functions are very good for code maintenance, but they incur a performance penalty of two pointer indirections. Say i have a base class with 2 subclasses(X and Y) and one virtual function, so there will be two virtual tables. The object has a pointer, based on which it will choose a virtual table. So for the compiler, it is more like switch( object's function ptr ) { case 0x....: X->call(); break; case 0x....: Y->call(); }; So why should virtual function cost more, if it can get implemented this way, as the compiler can do the same in-lining and other stuff here. Or explain me, why is it decided not to implement the virtual function execution in this way? Thanks, Gokul.

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• What's the difference between utf8_general_ci and utf8_unicode_ci

  - by KahWee

  Between utf8_general_ci and utf8_unicode_ci, are there any differences in terms of performance?

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• What are all the disadvantages of using files as a means of communicating between two processes?

  - by Manny

  I have legacy code which I need to improve for performance reasons. My application comprises of two executables that need to exchange certain information. In the legacy code, one exe writes to a file ( the file name is passed as an argument to exe) and the second executable first checks if such a file exists; if does not exist checks again and when it finds it, then goes on to read the contents of the file. This way information in transferred between the two executables. The way the code is structured, the second executable is successful on the first try itself. Now I have to clean this code up and was wondering what are the disadvantages of using files as a means of communication rather than some inter-process communication like pipes.Is opening and reading a file more expensive than pipes? Are there any other disadvantages? And how significant do you think would be the performance degradation. The legacy code is run on both windows and linux.

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• Architectural decision : QT or Eclipse Platform ?

  - by umanga

  We are in the process of designing a tool to be used with HDEM(High Definition Electron Microscope).We get stacks of 2D images from HDEM and first step is 'detecting borders' on the sections.After detecting edges of 2D slices ,next step is construct the 3D model using these 2D slices. This 'border detecting' algorithm(s) is/are implemented by one of professor and he has used and suggests to use C.(to gain high performance and probably will parallelise in future) We have to develop comprehensive UI ,3D viewer ,2D editor...etc and use this algorithm. Application should support usual features like project save/open.Undo,Redo...etc Our technology decisions are: A) Build entire platform from the scratch using QT. B) Use Eclipse Platform Our concerns are, if we choose A) we can easily integrate the 'border detecting' algorithm(s) because the development environment is C/C++ But we have to implement the basic features from the scratch. If we choose B) we get basic features from the Eclipse platform , but integrating C libraries going to be a tedious task. Any suggestions on this?

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• Ngram IDF smoothing

  - by adi92

  I am trying to use IDF scores to find interesting phrases in my pretty huge corpus of documents. I basically need something like Amazon's Statistically Improbable Phrases, i.e. phrases that distinguish a document from all the others The problem that I am running into is that some (3,4)-grams in my data which have super-high idf actually consist of component unigrams and bigrams which have really low idf.. For example, "you've never tried" has a very high idf, while each of the component unigrams have very low idf.. I need to come up with a function that can take in document frequencies of an n-gram and all its component (n-k)-grams and return a more meaningful measure of how much this phrase will distinguish the parent document from the rest. If I were dealing with probabilities, I would try interpolation or backoff models.. I am not sure what assumptions/intuitions those models leverage to perform well, and so how well they would do for IDF scores. Anybody has any better ideas?

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• Refactor/rewrite code or continue?

  - by Dan

  I just completed a complex piece of code. It works to spec, it meets performance requirements etc etc but I feel a bit anxious about it and am considering rewriting and/or refactoring it. Should I do this (spending time that could otherwise be spent on features that users will actually notice)? The reasons I feel anxious about the code are: The class hierarchy is complex and not obvious Some classes don't have a well defined purpose (they do a number of unrelated things) Some classes use others internals (they're declared as friend classes) to bypass the layers of abstraction for performance, but I feel they break encapsulation by doing this Some classes leak implementation details (eg, I changed a map to a hash map earlier and found myself having to modify code in other source files to make the change work) My memory management/pooling system is kinda clunky and less-than transparent They look like excellent reasons to refactor and clean code, aiding future maintenance and extension, but could be quite time consuming. Also, I'll never be perfectly happy with any code I write anyway... So, what does stackoverflow think? Clean code or work on features?

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